Conventionally, a printing plate is used for relief printing, intaglio printing, and lithographic printing on an object to be printed such as a packing material, a label, and a magazine. A relief printing plate is used for the relief printing. As a relief printing plates, a flexographic printing plate can be applied to printing on various objects to be printed because of its flexibility.
A flexographic printing plate precursor comprises a photosensitive layer made of a photosensitive resin composition on a substrate consisting such as of a PET resin. A flexographic printing plate is prepared by forming a relief image on the precursor. To form the relief image, the photosensitive layer is exposed to ultraviolet rays through a negative film contacted with the photosensitive layer and then uncured portions of the photosensitive layer are removed. Recently, the relief image is often formed by water development, in which the uncured portions are removed via the medium of water.
As an example of a water-developable photosensitive resin composition, PTL1 discloses a photosensitive resin composition comprising a water-dispersible latex, a photopolymerizable monomer, a rubber, and a photopolymerization initiator. As another example, PTL2 discloses a photosensitive resin composition comprising a water-soluble or water-swelling polymer, an ethylenic unsaturated compound, a photopolymerization initiator, and a sulfonate surfactant.